This invention relates generally to lifting devices in which a platform is elevated with respect to a fixed base by use of a hydraulic cylinder and a four-bar linkage; more specifically, it relates to an apparatus in which a platform is adapted to be attached to the frame of a truck, so that the platform may be selectively raised and lowered with respect to the truck's frame.
There are many instances in which a heavy load needs to be raised and lowered at a selected time and place and without the use of manual labor. A very common example of this requirement may be found at major airports, where goods are loaded onto a platform at something close to ground level and subsequently unloaded onto an aircraft at a substantially higher level. The highly specialized--and expensive--vehicles that perform this task are exemplified by the vehicles shown in U.S. Pat. No. 2,379,094 to Glenway Maxon Jr. entitled "Air Freight Handling System." The Maxon patent perhaps demonstrates, as well as can be done, that if there is a will to accomplish some task, and there is no limit on the amount of money that can be spent, then specialized equipment can be designed and built to do most any job.
There are frequent occasions, however, where the cost to design, build and maintain a vehicle with lifting capability is significantly restrained by budget considerations. In fact, there are many instances in which a company might like to have a vehicle with a movable platform on occasions, but the company cannot justify the expense of purchasing and maintaining a vehicle that cannot be used one-hundred percent of the time. Of course, many rental yards have been established and have grown on the basis of making exotic or specialized equipment available for short-term rental to companies that only occasionally need a specialized piece of equipment. One disadvantage to using rental equipment only on a "when-needed" basis is that the equipment may have already been rented to another party on the one day that a company needs it. Hence, it would be desirable to have a piece of lifting equipment available one-hundred percent of the time but at a modest cost, so that a company could afford to have its own equipment available whenever it is needed.
One example of a situation in which a heavy-duty lifting platform is desirable is when a load must be delivered to or received from a warehouse that has only conventional (high) loading docks. Such docks are designed for handling merchandise that is delivered with large vehicles, such as trailers that form parts of multi-wheel (e.g., 18-wheel) tractor/trailer rigs, and are conventionally placed at a height of about 48 inches above ground level. When a trailer or heavy truck is backed up to such a dock, conventional load-handling equipment that is routinely used within a warehouse (e.g., fork-lift trucks and pallet jacks) can be utilized to load and unload goods, because they can roll directly onto the bed of the relatively high trailer or truck.
However, there are also many instances in which the volume of a particular load does not justify the use of a large truck or trailer, even though the weight of the load makes it impractical to try to handle it by hand. For example, a load consisting of a large casting, an engine, a pump, or a pallet of hardware may occupy only a few cubic feet--but weigh 500 pounds. Such a load might be impractical to handle manually because of safety, time and other considerations. It would be desirable, therefore, if a light-weight truck (such as a half-ton, three-quarter ton, or one-ton pickup truck or the like) could be utilized to receive and transport a 900-pound load on a pallet, and then deliver that load to another high dock without requiring any manual handling of the load. Unfortunately, the customary height for lowered tail gates on a full-size pickups in the United States is about 30 to 36 inches. Hence, there can often be an elevation difference of about 20 inches between the bed of a pickup and a standard commercial dock; and there is no conventional warehouse equipment that can safely and dependably lower heavy loads a distance of 20 inches below a dock--unless it is a conveyor or ramp that is many feet in length. There has remained a need, therefore, for some mechanism that could dependably handle a load of several hundred, or even a few thousand, pounds, and move that load--in elevation--a distance of 20 or more inches. With such a mechanism, a conventional pickup truck rated at one-half to one ton could be utilized to handle goods that must be transferred onto a conventional "high" loading dock. It is an object of this invention to provide such a mechanism.
It is another object to provide an accessory that can be selectively attached to, and removed from, the bed of a truck without imposing any exotic requirements on the truck, so that standard commercial trucks can be utilized as the prime mover for the apparatus contemplated herein.
One more object is provide an accessory for a pickup truck or van that occupies relatively little space, so that the pickup or van can still be utilized in a conventional manner when the lifting platform is not required.
These and other objects will be apparent from a careful reading of the specification and claims, and the drawing that is attached hereto.